A vascular aneurysm typically occurs when there is localized stretching or distension of an artery due to a weakening of the vessel wall. The vascular distension itself is often referred to as an aneurysm sac. The opening from the vessel to the aneurysm sack is often referred as the aneurysm neck. Often an aneurysm can be the site of internal bleeding and, if the aneurism ruptures, the site of a stroke.
Several methods for treating aneurysms have been attempted, with varying degrees of success. For example, surgical or extravascular approaches are common in the treatment of intra-cranial berry aneurysms; these are straightforward but fairly traumatic. The method involves removing a portion of the cranium and locating the aneurysm. The neck of the aneurysm is typically closed by applying a specially sized clip to the neck of the aneurysm. The surgeon may choose to perform a suture ligation of the neck or wrap the entire aneurysm. Each of these procedures is performed by a very intrusive invasion into the body and is performed from the outside of the aneurysm or target site. General anesthesia, craniotomy, brain retraction, and a placement of clip around the neck of the aneurysm all are traumatic. The surgical procedure is often delayed while waiting for the patient to stabilize medically. For this reason, many patients die from the underlying disease prior to the initiation of the surgical procedure.
Another procedure, the extra-intravascular approach, involves surgically exposing or stereotaxically reaching an aneurysm with a probe. The wall of the aneurysm is perforated from the outside and various techniques are used to occlude the interior of the aneurysm to prevent it from bleeding. The techniques used to occlude the aneurysm include electro-thrombosis, adhesive embolization, hoghair embolization, and ferromagnetic thrombosis.
Alternative treatments include endovascular occlusion, in which the aneurysm is entered with a guidewire or a microcatheter, which is then used to emplace an occluding means. The occluding means is typically an embolic device, such as one or more coils or other devices, or an amount of an in situ polymerizable compound. An occlusion is formed within the sac, which is intended to reduce blood flow into the aneurysm. Because items are being placed in the aneurysm sack, there is a risk that the sac will be overfilled; that some of emplaced devices may migrate into the parent vessel; and/or that the aneurysm sack may be damaged during the process. Aneurysms that have a wide opening between the aneurysm sac and the parent vessel are particularly difficult to treat.
Another disadvantage of detachable coils involves coil compaction over time. After filling the aneurysm, there remains space between the coils. Continued hemodynamic forces from the circulation act to compact the coil mass resulting in a cavity in the aneurysm neck. Thus the aneurysm can recanalize. In addition, aneurysms that have a wide opening between the aneurysm sac and the parent vessel are difficult to treat. This is particularly true of bifurcation aneurysms such as basilar tip aneurysms.
Another means for forming an occluding mass in an aneurysm sac involves the placement of an elastic inflatable disc in the aneurysm. Detachable occlusion inflatable discs are used in many types of medical procedures. These inflatable discs are typically carried at the end of a catheter and, once inflated, are detached from the catheter. Such an inflatable disc may be positioned within an aneurysm, filled and then detached from the catheter. Besides delivery complications, elastic inflatable discs may be subject to overfilling, which may rupture the aneurysm. Likewise, if the inflatable disc is under-filled, the result may be incomplete occlusion of the aneurysm.
Conventional detachable balloons also suffer disadvantages. For example, detachable balloons, when inflated, typically do not conform to the interior configuration of the aneurysm sac. Instead, the detachable balloon requires the aneurysm sac to conform to the exterior surface of the detachable balloon. Thus, there is an increased risk that the detachable balloon will rupture the sac of the aneurysm. Further, because they engage the aneurysm only poorly, detachable balloons can rupture and migrate out of the aneurysm.
Another means for treating vascular aneurysms involves the placement of a liner in the aneurysm sac. An aneurysm liner includes a liner sac that is placed in the aneurysm sac and filled so as to occlude the aneurysm. A guidewire is typically utilized to carry the liner through the vasculature and to assist in deploying the liner in the aneurysm. While the aneurysm liner concept is intuitively attractive, it has posed a number of technical challenges. One primary challenge involves the difficulty in producing a material that is robust enough to contain embolic material without inhibiting the ability of the embolic device to conform to the aneurysm geometry itself, rather than the geometry of the liner. In many instances, materials currently incorporated into aneurysm liner concepts are not compliant enough to adequately remodel the neck portion of an aneurysm sac. This disadvantage can lead to neck remnants and subsequently recanalization after embolization.
Most current aneurysm liners are physically inconvenient or inappropriate for treatment of large aneurysms. For example, many liner concepts involve forming the aneurysm liner of a woven or braided polymeric material such as polypropylene or polyester. These mesh materials are difficult to use in treating medium to large size aneurysms, for example, aneurysms 5-20 millimeters in diameter. Such mesh materials result in an assembly that is too bulky when collapsed down into the catheter for delivery. In other words, the amount of liner material required to fill a relatively large aneurysm is very difficult to collapse down into a constrained, low profile, delivery configuration small enough to be delivered and deployed without excess friction on the walls of the delivery catheter or other delivery lumen. The bulkiness of these devices makes them inconvenient or inappropriate for intra-cranial delivery.
Various other methods and devices are known in the art. However, currently none produces a satisfactory method for closing the aneurysm opening. Thus, it remains desirable to provide devices that can readily and consistently be placed in an aneurysm opening so as to close the opening without damaging the vessel or risking damage to the aneurysm sack.